Radio volume control



Nov. 29, 1949 H. M. DRESSEL RADIO VOLUME CONTROL 2 Sheets-Sheet 1 Filed Oct. 15, 1947 INVENTOR. HE/VRY M DRESSEL.

BY 4 6W, (0% (jib/e5 M i; r roe/v5 Ys.

NOV. 1949 H. M. DRESSEL 2,439,757

RADIO VOLUME CONTROL Filed Oct. 15, 1947 2 Sheets-Sheet 2 gig; 4 INVENTOR.

Have) M 0/?ESSEL.

Patented Nov. 29, 1949 2,489,757 RADIO VOLUME CONTROL Henry M. Dressel, St. Marys, Pa.,

assignor to Stackpole Carbon Company, St. Marys, Pa., a corporation of Pennsylvania Applieationflctober 15, 1947, Serial No. 780,069

7 Claims. 1

This invention relates to electric circuit controls, such as volume and tone controls and the like, for radios.

It is among the objects of this invention to provide an electric circuit control in which the pressure of the sliding contact against the resister can be controlled, in which a good electrical connection is maintained between the sliding contact and the stationary contact connected to it, in which the resistance of the control shaft to turning does not depend upon the friction between the sliding contact and the resistor. Another object is to provide a satisfactory dual control of very small size.

In accordance with this invention a base member is provided with a central opening around which an arcuate resistor is mounted. A control shaft is rotatably mounted in the opening with its inner end projecting a short distance from the resistor side of the base. The projecting end of the shaft carries a collar and a metal head that rotate with it. The head is provided with an integral hub projecting toward the collar, and with a contact finger slidably engaging the iresistor. Encircling the hub is a wire loop formed at one end of a spring wire. The other end of the wire is connected to the base by a terminal member in a plane offset from the plane of the hub. This causes "the wire :loop to cant between the collar and metal head and thereby to exert pressure continuously against them at diametrically opposite points. This not only produces good electric contact between the loop and head, but also friction between the wire and collar to resist turning of the shaft. This friction in dual controls is sufficient to prevent either shaft from turning the other. The hub spaces the wire loop from the shaft and also makes the metal head rigid so that it will not bend when it is mounted on the shaft and thereby vary the pressure of the contact finger against the resistor.

The preferred improvement of the invention is illustrated in the accompanying drawings in which Fig. 1 is an enlarged side view of my volume control with its housing broken away; Fig. 2 is a horizontal section taken on the line II--II of Fig. 1; Fig. 3 is a vertical section taken on the line III-III of Fig. 2; Fig. 4 is a fragmentary horizontal section taken on the line IV--IV of Fig. 1; and '5 is a side view of a dual control utilizing the principles of this invention.

Referring to the drawings, an insulating base I is provided with a central opening from the bottom of which o. threaded bushing 2 extends.

j from a thin sheet metal head i2 Rotatably mounted in the bushing and extending some distance below it is a metal control shaft 3 adapted to receive the usual knob (not shown) on its lower end. The shaft projects a short distance above the base, but most of its projecting portion has been cut away from opposite sides to form a narrow central portion 5 (Figs. 3 and 4) having parallel sides. Mounted on the base and extending almost completely around the upper end of the shaft is a flat resistor element the ends of which are connected to terminal members 53 and i riveted to the base.

As shown in Fig. 3, the upper end of the shaft at the base of its thin portion is reduced slightly to form a shoulder on which a small metal washer 8 rests in order to increase the diameter of the shaft at this point. Resting on top of this washer and projecting laterally from it is a thin collar 9 of insulating material which is provided with a rectangular opening through which the fiattened portion 5 of the shaft extends. The collar, therefore, must turn with the shaft. The top of the collar, some distance from its outer edge, is engaged by a hub i l which has been struck down that is provided with a large central opening so that the hub is spaced from the control shaft. To hold the con trol head in proper position on the shaft without touching it, opposite sides of the head are provided with up-turned lugs 83 (Figs. 1 and 2) that extend through notches in the opposite ends of an elongated insulating member Hi. This member has a small central rectangular opening for snugly receiving the reduced upper end of the shaft. The insulating member, therefore, supports the control head from the shaft and compels the head to turn with the shaft. The insulating member and head are locked on the shaft by means of a metal plate is through which the end of the shaft projects and over which the shaft end is upset. Projecting toward each other from opposite sides of the control head is a pair of spring contact fingers i! having down-turned ends that engage and slide upon the resistor.

It is a feature of this invention that the metal control head it is electrically connected in an improved manner to a third terminal 22 fas-' tened to the base between terminals 6 and 7. Accordingly, a sprin wire 22 is provided at its outer end with a small hook shape portion that is held against the central terminal by the rivet 23 which fastens that terminal to the base. The wire extends inward between the ends of the arcuate resistor and has its inner end formed into a loop 24 that almost completely encircles the hub I l of the control head as shown in Fig. 4. The loop fits around the hub in the space between the control head and collar, although it need not be a snug fit. Th diameter of the wire preferably is slightly less than the depth of the hub.

As the top of collar 9 is a material distance above the level at which the outer end of wire 22 is attached to the base, the straight portion of the wire will be inclined as shown in Figs. 1 and 3. However, as the control head presses down on the loop 24 and keeps it from being inclined at the same angle as the straight portion, the wire will be bent down against the collar at the point nearest the central terminal. At the same time the diametrically opposite portion of the loop will press upward against the bottom of the metal head at about the point where the head and the hub come together. In other words. because the opposite end portions of the wire are held in different vertically spaced planes, the loop is caused to cant between the collar and head. One of the advantages of this is that the loop is always pressed tightly against the head to provide good electrical contact between them. The area of contact is well protected from dust and dirt. Another advantage is that th pressure of the wire against the rotatabl collar provides the friction necessary to hold the control shaft in any position to which it is turned, regardless of how light the pressure of the contact fingers against the resistor may be. A spring wire of this shape is inexpensive and requires but little space in the control, which is important for small controls with a large arc of rotation.

Also, with this construction in which the control head is provided with a hub, the hub makes the head rigid enough that it will not be deformed when the upper end of the shaft is upset to lock the head in place. As a result, the pressure that the spring fingers exert against the resistor can be predetermined and will not differ materially from unit to unit when the units are assembled. This pressure can be very light, which is desirable, because it is not depended upon to furnish the friction for holding the fingers in different positions along the length of the resistor. That function is performed by the pressure of the wire against the collar.

The invention is particularly useful in dual controls where two control units are mounted in tandem because of lack of space. In such controls one unit may control volume and the other tone. A dual control is shown in Fig. where unit as controls volume and the operation of an electric switch 21 mounted on it, while unit 28 controls the tone of a radio. Units 26 and 28 have essentially the same construction as disclosed in Figs. 1 to 4, including the wire 22 with the canted loop 25. The principal difference is that the rotatable control shaft 29 of unit 28 is a hollow sleeve, and that the rotatable control shaft 38 of unit 26 extends through the sleeve and projects from its outer end. The shafts must fit together rather snugly, to avoid side movement. The outer ends of the two shafts are adapted to receive separate control knobs so that either shaft may be turned independently of the other as is customary with dual controls. lit is very important that when either shaft is turned, its movement will not turn the other. Herctofore, it has been necessary to provide friction washers for the two shafts in order to prevent one shaft from turning the other. With this invention, however, the friction provided by the engagement of each wire 22 with the adjoining rotatable collar 9 keeps either shaft from turning except when it is turned by its knob. This makes it unnecessary to employ friction washers, and saves space where space is at a premium.

According to the provisions of the patent statutes, I have explained the principle and construction of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. An electric circuit control comprising a base provided with a central opening, an arcuate resistormounted on said base around said opening, a control shaft rotatably mounted in said opening with its inner end projecting a short distance from the resistor side of the base, a collar mounted on said projecting end of the shaft, a metal head rigidly mounted on the shaft and provided with an integral hub projecting toward said collar, said head having a contact member slidably engaging the resistor, a spring wire provided at one end with a loop encircling said hub and having sliding contact with the head, and a terminal member connecting the other end of the wire to the base in a plane offset from the plane of said hub, whereby the wire loop tends to cant between said collar and metal head to form good electrical contact with the head.

2. .An electric circuit control comprising an insulating base provided with a central opening, an arcuate resistor mounted on said base around said opening, a metal control shaft rotatably mounted in said opening with its inner end projecting a short distance from the resistor side of the base, an insulating collar mounted on said projecting end of the shaft, a metal head rigidly mounted on the shaft and provided with an integral hub spaced from the shaft and projecting toward said collar, said head having a resilient contact finger slidably engaging the resistor, a spring wire provided at one end with a loop encircling said hub and having sliding contact with the head, and a terminal member connecting the other end of the wire to the base in a plane offset from the plane of said hub, whereby the wire loop tends to cant between said collar and metal head to form a good electrical contact with the head.

3. An electric circuit control comprising a base provided with a central opening, an arcuate resistor mounted on said base around said opening, a control shaft rotatably mounted in said opening with its inner end projecting a short distance from the resistor side of the base, a collar mounted on said projecting end of the shaft and spaced from the plane of the resistor, a metal head rigidly mounted on the shaft and provided with an integral hub engaging said collar, said head having a contact member slidably engaging the resistor, a spring wire provided at one end with a loop encircling said hub and having sliding contact with the head, and a terminal member connecting the other end of the wire to the base between the ends of the arcuate resistor, whereby the wire loop tends to cant between said collar and metal head to form good electrical contact with the head.

4. An electric circuit control comprising a base provided with a central opening, an arcuate resistor, mounted on saidbase around said opening,

the resistor, a spring wire provided at one end I with a loop encircling said hub and having sliding contact with the head, and a terminal member connecting the other end of the Wire to the base in a plane offset from the plane of said hub, whereby the wire loop tends to cant between said collar and metal head to form good electrical contact with the head.

5. An electric circuit control comprising an insulating base provided with a central opening, an

arcuate resistor mounted on said base around said opening, a metal control shaft rotatably mounted in said opening with its inner end projecting a short distance from the resistor side of the base, an insulating collar mounted on said projecting end of the shaft and spaced from the plane of the resistor, a sheet metal head provided with a central shaft-receiving hole encircled by an outstruck hub spaced from the shaft and en gaging said collar, an insulating member secured to said head and rigidly mounted on the shaft,

the head having an integral resilient contact finger slidably engaging the resistor, a spring wire provided at One end with a loop encircling said hub and having sliding contact with the head, and a terminal member connecting the other end of the wire to the base between the ends of the arcuate resistor, whereby the wire loop tends to cant between said collar and metal head to form good electrical contact with the head.

6. An electric circuit control comprising an insulating base provided with a central opening, an arcuate resistor mounted on said base around said opening, a metal control shaft rotatably mounted in said opening with its inner end projecting a short distance from the resistor side of the base, said inner end of the shaft having a non-circular portion, a collar non-rotatably mounted on said portion of the shaft, a metal head rigidly mounted on said portion of the shaft and provided with an integral hub engaging said collar, said head having a contact member slidably engaging the resistor, a spring wire provided at one end with a loop encircling said hub and having sliding contact with the head, and a terminal member connecting the other end of the wire to the base in a plane offset from the plane of said hub, whereby the wire loop tends to cant between said collar and metal head to form good electrical contact with the head.

7. A dual control for radio circuits, comprising a pair of control units rigidly connected in axial alignment, each unit having a base provided with a central opening, an arcuate resistor mounted on said base around said opening, a control shaft rotatably mounted in said opening with its inner end projecting a short distance from the resistor side of the base, one of said shafts being tubular and the other shaft extending through it and projecting from its outer end, a collar mounted on said inner end of each shaft, a metal head rigidly mounted on the shaft and provided with an integral hub projecting toward said collar, said head having a contact member slidably engaging the resistor, a spring wire provided at one end with a loop encircling said hub and having sliding contact with the head, and a terminal member connecting the other end of the wire to the base in a plane offset from the plane of the hub, whereby each wire loop tends to cant between the adjoining collar and metal head and thereby presses against the collar to produce friction that will keep the adjoining shaft from turning the other shaft.

HENRY M. DRESSEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,997,427 Mucher Apr. 9, 1935 2,177,291 Schellenger Oct. 24, 1939 2,266,188 Foley et a1 Dec. 16, 1941 2,311,611 Nied Feb. 16, 1943 2,401,037 Arvin May 28, 1946 

